1/2" out of plumb for a door is a heck of a lot. You've checked everything around it (wall, floor, etc) to see that everything else is correct? I'm surprised that the door will close at all that much out of plumb. Do you know any carpenters that could take a look at it?
Do you know if your dealer is good at doing repairs like that? Because, if you are having no other issues with the camper, maybe you don't want them working on the door (and maybe causing more problems). Does your warranty last into next season? Maybe wait a bit to see if anything comes up the dealer may have to fix.
We always travel with the bathroom door closed. Usually always have it open when camping (unless someone is using it!), to allow for venting when we use the fan in the bathroom skylight.